1. Field of the Invention
The present invention relates to the field of medical radiography, and more particularly to means for positively identifying the exposure side or front side of an x-ray film.
2. Description of the Prior Art
A medical radiograph is the x-ray image of some part of the body produced by an x-ray beam originating from an x-ray tube, passing through the body part, and then striking an x-ray film. During exposure the x-ray film is typically contained within a cassette which is a light-proof, flat box of rigid construction.
X-ray film, like photographic film, is generally comprised of a sheet of translucent supporting material called the base which is coated on one or both sides with a photosensitive emulsion. This photosensitive emulsion can be activated (or sensitized) by exposure to photons of different wavelengths within the electromagnetic spectrum, including the visible light band and the x-ray band. The sensitivity of the film emulsion to photons varies with the wavelength of the photons and is generally far more sensitive to photons in the visible band of the spectrum than in the x-ray band of the spectrum. Activation produces a latent effect on the emulsion which, when the film is developed, appears as a relative darkening of the emulsion proportional to the amount of exposure. A part of the body interposed between the x-ray beam and the film absorbs the x-ray beam in variable degrees depending on the internal structure of the part x-rayed. This differential exposure of the film results in a pattern of light and dark corresponding to the anatomy of the part x-rayed and constitutes the medical radiograph.
Since it is generally desirable that the medical radiograph be provided with pertinent identifying information such as the patient's name, date, etc., means must be provided to transmit such data to the film. This is accomplished in various ways. The technologist can simply write this information directly on the film surface or attach a label containing such data, usually after the film is processed. However this lends itself to possible error, particularly in larger departments, and has generally been superseded by methods of identification carried out at the time of exposure or before processing. The prior art describes several methods whereby the identification is carried out by radiographic means (see U.S. Pat. No. 3,518,428 to Ring; U.S. Pat. No. 4,035,653 to Karasko; U.S. Pat. No. 3,668,394 to Panzer; and U.S. Pat. No. 4,127,774 to Gillen). All of these describe means by which the desired information is fashioned into radiopaque indicia which is positioned on the front surface of the x-ray cassette whereby it intercepts and absorbs a portion of the x-ray beam used to produce the anatomic image. This data is transmitted simultaneously with the anatomic information creating the radiographic image through the cover of the closed cassette and causes an image of the data to appear on the enclosed film along with the image of the body part x-rayed. Thus a single radiographic exposure creates both the medical radiograph and image of the identification data on the film.
Film identification systems wherein patient data is conveyed to x-ray film by visible and near visible light, that is light having wavelengths ranging from 1.times.10.sup.-7 meters to 1.times.10.sup.-6 meters, are referred to as "photographic" systems. Such photographic systems differ from "radiographic" systems, wherein data is conveyed to the film by x-ray radiation, in that photographically conveyed data can be more quickly and easily generated than data conveyed by x-ray radiation. As a consequence, virtually all cassettes in use today use photographic means, and not radiographic means, to provide x-ray film with patient data. X-ray cassettes, appointed for use in photographic film identification systems, are provided with a "blocker". This blocker is generally comprised of one or two rectangular strips of lead mounted on the cassette that shield a preselected area of film between the two blockers from becoming exposed by the effect of the x-ray beam. Prior to development of the sheet of film, patient identification data contained on a card or piece of paper is projected by a beam of light onto the area of the film shielded from x-ray exposure by the blocker. A latent image of the data is formed within the rectangular area of film shielded by the blockers, and becomes visible when the film is developed. This identification rectangle is about 3 square inches. The position of the blocker within the cassette is not necessarily consistent, even within the same x-ray department, and may vary with the manufacturer, cassette type, or type of film identification system used. The exact manner in which the data is projected onto the film varies with the type of identification device employed.
Generally a beam of light is used to convey the data from the card containing it to the area of the undeveloped film appointed to receive such data. Thereby an image of the data is created that becomes visible when the film is developed. Device and methods, including modifications of the film cassette for marking exposed film or radiographs with patient data are disclosed, for example by U.S. Pat. Nos. 3,628,864, 3,703,272, 4,465,364, 4,510,392, 4,806,959, 4,383,329, 4,520,497, and 4,768,114.
When rendering a diagnosis from a radiograph it is necessary for the film viewer to know which side of the body is being viewed. Since the body is generally symmetrical, right-sided structures are similar in appearance to left-side structures except that they are mirror images or reversals of one another. For example, an x-ray image of a left foot if viewed from the back of the exposed film will look like a right foot. Since radiographs are typically transparent and can be viewed from either side, it is therefore possible for x-ray images of one side of the body to become confused with the other. For this reason when a medical radiograph is performed of some part of the body it is customary for the technologist to affix a lead "R" or "L" marker on the cassette surface adjacent to the part being x-rayed. This indicates which side of the body is represented on the film. Not infrequently however, the technologist places the wrong lead marker on the cassette or for one reason or another its image is not visible on the film, being either obscured or omitted. When this happens, the technologist then needs to mark the film after it is developed, using an adhesive label, wax pencil, ink, or other means. The incidence of incorrect or absent right/left marking due to human error is quite substantial, reportedly as high as 30%. If the film is improperly marked and the physician interpreting the film recognizes the error he will often try to locate the technologist who performed the study to obtain clarification. When the question cannot be resolved in this manner, the patient may be recalled for a repeat examination that involves time, inconvenience, expense and additional radiation exposure. Furthermore, if the error should go undetected, incorrect medical treatment may result.
Various film identification systems exist to provide means for the patient data to be included on the radiograph. In one such system, patient data is entered on a card that, in the dark room, is placed into the device to thereby approximate the surface of an undeveloped x-ray film sheet. The card is then transilluminated by a light beam that passes through the card, thereby projecting the image of the patient data onto the identification rectangle of film in the manner of a contact print. Depending on the particular type of device used or the manner in which the card is inserted, the image of the patient date may be presented on the developed film reading in either a forward or reversed orientation. If the card is inadvertently inserted with the wrong face up, the image of the patient data is presented on the developed film in reversed orientation.
Another type of film identification device, disclosed by U.S. Pat. No. #3,628,864 to Fessenden et al., illuminates the face of a card by a light source and optically projects patient data from the card face onto the film identification rectangle by means of lens system. Such a system is marketed by KODAK under the name "X-OMATIC IDENTIFICATION CAMERA". The patient data card is placed face-down over an aperture in a camera. When the undeveloped x-ray film is ready for identification, the cassette in which the film is contained, is placed face-down onto a cassette receiver and firmly pressed against a switch, which causes a sliding panel in the back of the cassette to open, uncovering the film identification rectangle. A lens system optically projects data from the card onto the back of the film.
Still another type of identification device, is disclosed by U.S. Pat. No. #4,383,329 to Krobel et al. By means of an internal lens system, the device of Krobel et al., optically projects patient identification data from a card placed over an aperture in the device onto the identification rectangle of the undeveloped film. The Krobel et al., device also contains means for (1) reversing the orientation of the identification data, at the option of the operator, and (2) electronically generating and projecting additional data onto the film.
It is not possible to reliably identify the exposure side of an x-ray film from the direction the patient identification data reads or from the position of the identification blocker. For example, certain commercial film identification devices project patient identification data into the identification rectangle in an orientation which is readable from the exposure side of the film whereas other commercial film identification devices project the data in an orientation which is backwards when seen from the exposure side of the film. Furthermore it is possible for the card containing the data to be inserted upside down in some of such devices, altering the side of the film that the patient data can be read.
There remains a need in the art for a method and means operative to locate within the film identification area a marker that expressly and reliably indicates the exposure side of the film independent of the actions of the technologist and independent of the orientation of the patient identification area.